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<TITLE>
Jamfiles and Jambase
</TITLE>
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<CENTER>
<A HREF=http://www.perforce.com/jam/jam.html>
Jam
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<A NAME="TOP">
<H2>
Using Jamfiles and Jambase
</H2>
</A>
</CENTER>
<P>
This document describes how to write Jamfiles using the Jam Jambase 
rules to build software products. 
Related documents of interest are:
<UL>
<LI>
	<a href="Jam.html">The Jam Executable Program</A>,
	which describes using the <b>jam</b> command and the 
	langauge used in Jambase
<LI>
	<A href="Jambase.html">Jambase Reference</A>,
	which summarizes the Jambase rules and variables
</UL>
<P>
Jam documentation and source are available from the
<A HREF=http://public.perforce.com/public/index.html>Perforce Public Depot</a>.
<HR>
<P>
<H2>
Overview
</H2>
<P>
        <B>jam,</B> the Jam executable program,
       recursively  builds  target files  from source files
       using dependency and build specifications defined
       in Jam rules files.
        <B>jam</B> parses the rules files to identify targets
        and sources,
        examines the filesystem to determine which
        targets need updating, and issues OS commands to update
        targets.
<P>
        A base rules file called "Jambase" is provided with the 
	Jam distribution. 
	The Jambase file defines rules and variables which support
	standard software build operations, like compiling, linking,
	etc.
<P>
	When the Jambase rules are used,
	<B>jam</B> reads Jambase, then reads a file called
	"Jamfile" in the current directory.
	The Jamfile describes what to do with the source files in 
	its directory. It may also cause
	Jamfiles in other directories to be read. 
	<P>
	Under certain circumstances, the first Jamfile read
	also causes a site-specific "Jamrules" file to be read.
	The Jamrules file is an optional set of rule and variable
	definitions used to define site-specific processing.
<P>
<H4>
The Basic Jamfile
</H4>
<P>
Jamfiles contain rule invocations, which usually look like:
<PRE>
	<I>RuleName</I> <I>targets</I> : <I>targets</I> ;
</PRE>
The target(s) to the left of the colon usually indicate
what gets built, and the target(s) to the right of the
colon usually indicate what it is built from.
<P>
<P>
A Jamfile can be as simple as this:
<PRE>
	Main myprog : main.c util.c ;
</PRE>
This specifies that there is a main.c and util.c file in the same
directory as the Jamfile, and that those source files should be
compiled and linked into an executable called myprog.
If you cd to the directory where this Jamfile lives,
you can see the exactly how <b>jam</b> would 
build myprog with:
<PRE>
	jam -n
</PRE>
Or, you can actually build myprog with the command:
<PRE>
	jam
</PRE>

<P>
<H4>
Whitespace
</H4>
Jamfile elements are delimited by whitespace (blanks, tabs, or
newlines). Elements to be delimited include rule names, targets,
colons, and semicolons. A common mistake users make is to forget the
whitespace, e.g.,
<PRE>
	Main myprog: main.c util.c ; #<I>WRONG!</I>
</PRE>
Jam doesn't distinguish between a typo and a target called "myprog:", 
so if you get strange results, the first thing
you should check for in your Jamfile is missing whitespace.
<P>
<H4>
Filenames, Target Identifiers, and Buildable Targets
</H4>
<P>
Consider this Jamfile:
<PRE>
	Main myprog : main.c util.c ;                   
	LinkLibraries myprog : libtree ;     
	Library libtree : treemake.c treetrav.c ;    
</PRE>
<P>
The Main rule specifies that an executable called myprog will be built.
The compiled main.c and util.c objects will be linked to produce
myprog. 
The LinkLibraries rule specifies that libtree will
be linked into myprog as well.
The Library rule specifies which source files will be compiled and
archived into the libtree library.
<P>
The Jamfile above refers to targets like "myprog" and "libtree". 
However, depending on the platform you're building on, the actual
filenames of those targets could be "myprog.exe" and "libtree.lib".
Most Jambase rules supply the actual filenames of targets,
so that Jamfiles themselves need not make any
platform-specific filename references.
<P>
The <b>jam</b> program builds up a list of unique target identifiers.
Unless you are using the SubDir rules (described later),
the default identifier for a file target is its filename. In the above
example, the target identifiers are the filenames: myprog.exe,
libtree.lib, main.obj, etc.
<P>
While all Jambase rules refer to "targets",
not all targets are buildable.
There are two kinds of buildable targets: 
file targets and pseudotargets.
File targets are objects that can be found in the filesystem.
Pseudotargets are symbolic, and represent other targets.
<P>
You can use any buildable target on the <b>jam</b> command line to
build a subset of defined targets. For example:
<PRE>
        jam libtree.a 
</PRE>
on Unix builds the libtree library and all the compiled objects
that go in it.
<P>
<H4>
Pseudotargets
</H4>
<P>
Most Jambase rules that define file targets also define pseudotargets
which are dependent on types of file targets.
For example, Jambase defines a pseudotarget called "lib", which 
is dependent on file targets created by the Library rule. So 
the command:  
<PRE>
        jam lib
</PRE> 
used with the above example would cause the libtree library to be built.
Also, there is one pseudotarget built into <b>jam</b> itself, called
"all". Jambase sets "all" dependent on (almost) all other targets.
<P>
In the unfortunate case where you have a buildable target whose name
is the same as one of the Jambase pseudotargets, you'll have problems
with the conflicting target name.
Your workaround choices are:
<P>
<ol>
<lI>Change the name of your buildable file or directory that conflicts.
<p>
<li>Modify your Jambase and change the name of the conflicting pseudotarget.
(Pseudotargets are defined in Jambase using the NOTFILE rule.)
<p>
<li>Use grist on the conflicting target name in your Jamfile. E.g., instead
    of
    <PRE>
    File lib : libfoo.a ;
    </PRE>
    try
    <PRE>
    File &lt;dir&gt;lib : libfoo.a ;
    </PRE>
</ol>
<P>

<H4>
Dependencies
</H4>
<P>
Jambase rules set dependencies on targets, so that if you update a
source file, all the file targets that depend on that source
file, and only the ones that depend on that source file, 
will be updated (rebuilt) the next time you run <b>jam</b>. 
<P>
Here are some of the dependencies 
that get set when <b>jam</b> runs on NT using the example Jamfile above:
<CENTER>
<TABLE> 
<TR><TD><B>Target</B><TD>&nbsp;&nbsp;&nbsp;<TD><B>Depends on</B></TD>
<TR><TD>myprog.exe<TD><TD>main.obj, util.obj, libtree.lib
<TR><TD>libtree.lib<TD><TD>treemake.obj, treetrav.obj
<TR><TD>treetrav.obj<TD><TD>treetrav.c
</TABLE>
</CENTER>
<P>
Furthermore, the Main and Library rules set up recursive
header scanning on their source targets.
So after <b>jam</b> has finished parsing the Jamfile and
setting the rule-driven dependencies, it scans the source 
files for "#include" lines. All #include files found during
this scan become dependencies of the compiled object.
E.g., all header files used to compile treetrav.c would
be made dependencies of treetrav.obj.
<P>
As a result, when you run <b>jam</b>, it will rebuild targets
if either the source files change or the 
header files change. You can't tell by looking at a Jamfile
which header files are dependencies, but you can easily
display those dependencies with:
<PRE>
	jam -nd+3
</PRE>
<H4>
Rule Ordering
</H4>
<P>
Rules which specify dependencies, like the Main, Library, and
LinkLibrary rules, can be invoked in any order. <b>jam</b>
figures out the order in which targets are built from 
their dependencies.
<P>
Some rules, however, set variables which are used by subsequent
rule invocations, and their ordering is important. 
For example, the SubDir* rules (discussed
later) must be invoked in a particular order.

<P>
<H4>
Detailed Jambase Specifications
</H4>
<P>
This document describes how to use various Jambase rules
from a functional point of view.
You can see the summary of available Jambase rules in the
<a href="Jambase.html">Jambase Reference</A>.
The detailed specifications for any Jambase rule
can be found by reading the rule definition itself
in the Jambase file.
<P>

<HR>
<H2>
Handling Directory Trees
</H2>
       The SubDir* rules are used to
       define source code directory hierarchies.
       With SubDir and SubInclude, you can use <b>jam</b>
       to build software from source files and Jamfiles spread
       across many directories, as is typical for large projects.
       The SubDir* rules unify an entire
       source code tree so that <b>jam</b> can read in
       all the Jamfiles in one pass and 
       compute dependencies across the entire project.
<P>
	To use the SubDir* rules, you must:
<P>
<OL>
       <LI>     Preface the Jamfile in each directory with an invocation 
       of the SubDir rule.
<P>
       <LI>     Place  at  the  root  of the tree a file named Jamrules.  
	      This file could be empty,  but  in
              practice  it contains user-provided rules and variable 
	      definitions that  are  shared  throughout  the
              tree.   Examples  of  such  definitions are library
              names,  header  directories,  install  directories,
              compiler  flags,  etc.  This file is good candidate
              for automatic customizing with autoconf(GNU).
<P>
	<LI> 	Optionally, set an environment variable pointing
		to the root directory of the srouce tree. The
		variable's name is left up to you, but in these
		examples, we use TOP.
</OL>
<P>
<H4>
   SubDir Rule
</H4>
<P>
       The  SubDir  rule  must  be  invoked before any rules that
       refer to the contents of the directory - it is best to put
       it at the top of each Jamfile.  For example:
<PRE>
	# Jamfile in $(TOP)/src/util directory.

	SubDir TOP src util ;

	Main myprog : main.c util.c ;                   
	LinkLibraries myprog : libtree ;     
	Library libtree : treemake.c treetrav.c ;    
</PRE>
       This  compiles  four  files  in  $(TOP)/src/util, archives
       two of the objects into libtree, and links  the  whole
       thing into myprog. 
       Outputs are placed in the $(TOP)/src/util
       directory. 
       <P>
       This doesn't appear to be any different from 
       the previous example that didn't have a SubDir rule,
       but two things are happening behind the scenes:
       <OL>
       <LI>The SubDir rule causes <b>jam</b> to read
	   in the $(TOP)/Jamrules file. 
           (The Jamrules file can alternately be named by  the
              variable  $(xxxRULES), where xxx is the name of the
              root variable, e.g., $(TOPRULES)).  
	      <P>
	   The Jamrules file can contain variable definitions
	   and rule definitions specific to your codeline.
	   It allows you to completely customize your build 
	   environment without having to rewrite Jambase.
	   Jamrules is only read
	   in once, at the first SubDir invocation.
	   <P>
	<LI>
	   The SubDir rule initializes a set of variables
	   that are used by Main and other rules to 
	   uniquely identify the source files in this
	   directory and assign locations to the targets
	   built from files in this directory.
	   <P>
	   When you have set a root variable, e.g., $(TOP),
	   SubDir constructs path names rooted with $(TOP),
	   e.g., $(TOP)/src/util.
	   Otherwise, SubDir constructs relative pathnames
	   to the root directory, computed from the number
	   of arguments to the first SubDir rule, e.g.,
	   ../../src/util. In either case, the SubDir
	   rule constructs the path names that locate source
	   files.
	   You'll see how this is useful later.
	<P>
       </UL>

<P>
       The SubDir rule takes  as  its  first  argument  the  root
       variable's  name  and  takes  as  subsequent arguments the
       directory names leading from the root to the directory  of
       the  current Jamfile.  Note that the name of the subdirectory 
       is given as individual  elements:   the  SubDir  rule
       does not use system-specific directory name syntax.
<P>
<P>
<H4>
   SubInclude Rule
</H4>
	The SubInclude rule is used in a Jamfile to cause another
	Jamfile to be read in.
       Its arguments are in  the  same  format  as
       SubDir's.
<P>
       The  recommended  practice is only to include one level of
       subdirectories at a time, and let the Jamfile in each subdirectory  
       include  its own subdirectories.  This allows a
       user to sit in any arbitrary directory of the source  tree
       and build that subtree.  For example:
<PRE>
       # This is $(TOP)/Jamfile, top level Jamfile for mondo project.

       SubInclude TOP src ;
       SubInclude TOP man ;
       SubInclude TOP misc ;
       SubInclude TOP util ;
</PRE>
       If  a directory has both subdirectories of its own as well
       as files that need building,  the  SubIncludes  should  be
       either before the SubDir rule or be at the end of the Jamfile 
       - not between the SubDir and other rule  invocations.
       For example:
<PRE>
	# This is $(TOP)/src/Jamfile:

	SubDir TOP src ;

	Main mondo : mondo.c ;
	LinkLibraries mondo : libmisc libutil ;
	
	SubInclude TOP src misc ;
	SubInclude TOP src util ;
</PRE>
<P>
	(<b>jam</b> processes all the Jamfiles it reads as if
	it were reading one single, large Jamfile. 
	Build rules like Main and LinkLibraries rely on the
	preceding SubDir rule to set up source file and
	output file locations, and SubIncludes rules read in
	Jamfiles that contain SubDir rules. So if you put
	a SubIncludes rule between a SubDir and a Main
	rule, <b>jam</b> will try to find the source files
	for the Main rule in the wrong directory.)
<P>
<H4>
   Variables Used to Handle Directory Trees
</H4>
       The  following  variables are set by the SubDir rule
       and used by the Jambase rules that define file targets:
<P>
<CENTER>
<TABLE>
<TR><TD VALIGN=TOP>
              SEARCH_SOURCE
	      <TD><TD>The SubDir targets (e.g., "TOP src util")
	      are used to construct a pathname (e.g., $(TOP)/src/util),
	      and that pathname is assigned to $(SEARCH_SOURCE). 
	      Rules like Main and Library use $(SEARCH_SOURCE)
	      to set search paths on source files.
<TR><TD VALIGN=TOP>
              LOCATE_SOURCE
	      <TD><TD>Initialized by the SubDir rule to the same
	      value as $(SEARCH_SOURCE), unless ALL_LOCATE_TARGET
	      is set.
	      $(LOCATE_SOURCE) is used by rules that build
	      generated source files (e.g., Yacc and Lex) to
	      set location of output files.
	      Thus the default location of built source files
	      is the directory of the Jamfile that defines them.
<TR><TD VALIGN=TOP>
              LOCATE_TARGET
	      <TD><TD>Initalized by the SubDir rule to the same
	      value as $(SEARCH_SOURCE), unless ALL_LOCATE_TARGET
	      is set.
	      $(LOCATE_TARGET) is used by rules that build
	      binary objects (e.g., Main and Library) to
	      set location of output files.
	      Thus the default location of built binaray files
	      is the directory of the Jamfile that defines them.
<TR><TD VALIGN=TOP>
              ALL_LOCATE_TARGET
	      <TD><TD>
	      If $(ALL_LOCATE_TARGET) is set, LOCATE_SOURCE
	      and and LOCATE_TARGET are set to  $(ALL_LOCATE_TARGET)
	      instead of to $(SEARCH_SOURCE). This can be used to
	      direct built files to be written to a location outside
	      of the source tree, and enables building from read-only
	      source trees.
<TR><TD VALIGN=TOP>
              SOURCE_GRIST
	      <TD><TD>The SubDir targets are formed into a string
	      like "src!util" and that string is assigned to 
	      SOURCE_GRIST. Rules that define file targets
	      use $(SOURCE_GRIST) to set the "grist" attribute
	      on targets. This is used to assure uniqueness 
	      of target identifiers where filenames themselves
	      are not unique.
	      For example, the target identifiers of 
	      $(TOP)/src/client/main.c and $(TOP)/src/server/main.c
	      would be &lt;src!client&gt;main.c and &lt;src!server&gt;main.c.
</TABLE>
</CENTER>
<P>
       The $(LOCATE_TARGET) and  $(SEARCH_SOURCE)  variables are used
       extensively by rules in Jambase: most rules that  generate
       targets  (like  Main,  Object,  etc.)  set $(LOCATE) to 
       $(LOCATE_TARGET) for the targets they generate, and  rules
       that  use  sources  (most all of them) set $(SEARCH) to be
       $(SEARCH_SOURCE) for the sources they use.
<P>
       $(LOCATE) and $(SEARCH) are better  explained  in  
       <A HREF="Jam.html">The Jam Executable Program</A>
       but in brief they tell <B>jam</B> where to create new targets and
       where to find existing ones, respectively.
<P>
       Note that you can reset these variables
       after SubDir sets them. For example, this Jamfile builds
       a program called gensrc, then runs it to create a source file
       called new.c: 
       <PRE>
       SubDir TOP src util ;
       Main gensrc : gensrc.c ;
       LOCATE_SOURCE = $(NEWSRC) ;
       GenFile new.c : gensrc ;
       </PRE>
       By default, new.c would be written into the
       $(TOP)/src/util directory, but resetting LOCATE_SOURCE causes
       it to be written to the $(NEWSRC) directory. ($(NEWSRC) is assumed
       to have been set elsewhere, e.g., in Jamrules.)
<P>
<H4>
   VMS Notes
</H4>
       On VMS, the logical name table is not imported as  is  the
       environment on UNIX.  To use the SubDir and related rules,
       you must set the value of the variable that names the root
       directory.  For example:
<PRE>
              TOP = USR_DISK:[JONES.SRC] ;

              SubInclude TOP util ;
</PRE>
       The variable must have a value that looks like a directory
       or device.  If you choose, you can use a  concealed  logical.  
       For example:
<PRE>
              TOP = TOP: ;

              SubInclude TOP util ;
</PRE>
       The  :  at  the  end of TOP makes the value of $(TOP) look
       like a device name, which jam respects as a directory name
       and  will  use when trying to access files.  TOP must then
       be defined from DCL:
<PRE>
              $ define/job/translation=concealed TOP DK100:[USERS.JONES.SRC.]
</PRE>
       Note three things: the concealed  translation  allows  the
       logical  to  be  used as a device name; the device name in
       the logical (here DK100) cannot itself be concealed  logical  
       (VMS  rules, man); and the directory component of the
       definition must end in a period (more VMS rules).
<P>
<H2>
Building Executables and Libraries
</H2>
<P>
The rules that build executables and libraries are: Main, Library,
and LinkLibraries.
<H4>
   Main Rule
</H4>
       The Main rule compiles source files and links the  resulting 
       objects into an executable.  For example:
<PRE>
              Main myprog : main.c util.c ;
</PRE>
       This  compiles  main.c  and  util.c  and  links main.o and
       util.o into myprog. The object files and resulting 
       executable are named appropriately for the platform.
<P>
	Main can also be used to build shared libraries and/or
	dynamic link libraries, since those are also linked
	objects. E.g.:
	<PRE>
		Main driver$(SUFSHR) : driver.c ;
	</PRE>
	Normally, Main uses $(SUFEXE) to determine the suffix on
	the filename of the built target. To override it,
	you can supply a suffix explicity.
	In this case,
	$(SUFSHR) is assumed to be the OS-specific shared library
	suffix, defined in Jamrules with something
	like:
	<PRE>
		if $(UNIX)      { SUFSHR = .so ; }
		else if $(NT)   { SUFSHR = .dll ; }
	</PRE>
	<P>
	Main uses the Objects rule to compile source targets. 

<H4>
   Library Rule
</H4>
       The Library  rule  compiles  source  files,  archives  the
       resulting  object  files  into a library, and then deletes
       the object files.  For example:
<PRE>
              Library libstring : strcmp.c strcpy.c strlen.c ;
              Library libtree : treemake.c treetrav.c ;
</PRE>
       This compiles five source files,  archives  three  of  the
       object  files into libstring and the other two into libtree.  
       Actual library filenames are formed with the $(SUFLIB) suffix.
       Once the objects are safely in the libraries, the
       objects are deleted.
       <P>
       Library uses the Objects rule to compile source files.
<P>
<H4>
   LinkLibraries Rule
</H4>
       To link executables with built libraries, use
       the LinkLibraries rule.  For example:
<PRE>
              Main myprog : main.c util.c ;
              LinkLibraries myprog : libstring libtree ;
</PRE>
       The LinkLibraries rule  does  two  things:  it  makes  the
       libraries dependencies of the executable, so that they get
       built first; and it makes the libraries  show  up  on  the
       command  line  that links the executable.  The ordering of
       the lines above is not important, because <b>jam</b> builds  targets 
       in the order that they are needed.
<P>
       You  can  put multiple libraries on a single invocation of
       the LinkLibraries rule, or you can provide them in  multiple  
       invocations.   In both cases, the libraries appear on
       the link command line in the  order  in  which  they  were
       encountered.  You can also provide multiple executables to
       the LinkLibraries rule, if they need the same libraries,
       e.g.:
       <PRE>
		LinkLibraries prog1 prog2 prog3 : libstring libtree ;
       </PRE>
<P>
<H4>
   Variables Used in Building Executables and Libraries
</H4>
<CENTER>
<TABLE>
<TR><TD>
              AR           
	      <TD><TD>Archive command, used for Library targets.
<TR><TD>
              SUFEXE         
	      <TD>*<TD>Suffix on filenames of executables referenced
		by Main and LinkLibraries.
<TR><TD>
              LINK           
	      <TD><TD>Link command, used for Main targets.
<TR><TD>
              LINKFLAGS       
	      <TD><TD>Linker flags.
<TR><TD>
              LINKLIBS        
	      <TD><TD>Link libraries that aren't dependencies. (See note
		below.)
<TR><TD>
              EXEMODE         
	      <TD>*<TD>File permissions on Main targets.
<TR><TD>
              MODE            
	      <TD><TD>Target-specific file permissions on Main targets
		(set from $(EXEMODE))
<TR><TD>
              RANLIB          
	      <TD><TD>Name of ranlib program, if any.
</TABLE>
</CENTER>

<P>
	Variables above marked with "*" are used by the Main,
	Library, and LinkLibraries rules. Their values at the 
	time the rules are invoked are used to set target-specific
	variables.
	<P>
	All other variables listed above are globally defined,
	and are used in actions that update Main and Library
	targets. This means that the global values of those
	variables are used, uness target-specific values have
	been set. 
	(For instance, a target-specific MODE value is set by 
	the Main rule.)
	The target-specific values always override
	global values.
<P>
	Note that there are two ways to specify link libraries for
	executables: 
	<UL>
	<LI>Use the LinkLibraries rule 
	to specify built libraries; i.e., libraries
	that are built by Library rules. This assures that
	these libraries are built first, and that Main targets are 
	rebuilt when the libraries are updated.
	<P>
	<LI>Use the LINKLIBS variable to specify external
	 libraries; e.g., system libraries or third-party libraries.
	 The LINKLIBS variable must be set to the the actual
	 link command flag that specifies the libraries.
	 <P>
	 </UL>
	 <P>
	 For example:
<PRE>
	<I>#In Jamrules:</I>
              if $(UNIX) { X11LINKLIBS = -lXext -lX11 ; }
              if $(NT)   { X11LINKLIBS = libext.lib libX11.lib ; }

	<I>#In Jamfile:</I>
              Main xprog : xprog.c ;
              LINKLIBS on xprog$(SUFEXE) = $(X11LINKLIBS) ;
              LinkLibraries xprog : libxutil ;
              Library libxutil : xtop.c xbottom.c xutil.c ;
</PRE>
       This  example  uses the Jam syntax "variable on target" to
       set a target-specific variable.  In this way,  only  xprog
       will  be linked with this special $(X11LINKLIBS), 
       even if other executables were going to  be  built
       by  the  same Jamfile. Note that when you set a variable
       on a target, you have to specify the target identifer
       exactly, which in this case is the suffixed filename of
       the executable.
       The actual link command line on Unix, for example, would
       look something like this:
<PRE>
              cc -o xprog xprog.o libxutil.a -lXext -lX11
</PRE>
<H2>
Compiling
</H2>
       Compiling of source files occurs normally as  a  byproduct
       of  the Main or Library rules, which call the rules 
       described here. These rules may also be called explicitly
       if the Main and Library behavior doesn't satisfy your
       requirements.
<P>
<H4>
   Objects Rule
</H4>
       The Main and Library rules call the Objects rule on source files.
       Compiled object files built by
       the Objects rule are a dependency of the <I>obj</i>
       pseudotarget, so "jam obj" will build object files used in 
       Main and Library rules.
       <P>
       Target identifiers created by the Objects rule have grist
       set to $(SOURCE_GRIST). So given this Jamfile:
       <PRE>
		SubDir TOP src lock ;
		Main locker : lock.c ;
       </PRE>
       the object file created is lock.o (or lock.obj) and
       its target identifier is &lt;src!lock&gt;lock.o 
       (or &lt;src!lock&gt;lock.obj).

       <P>
       You can also call  Objects  directly.  For example:
<PRE>
              Objects a.c b.c c.c ;
</PRE>
       This compiles a.c into a.o, b.c into b.o, etc. The object
       file suffix is supplied by the Objects rule.
<P>
<H4>
   Object Rule
</H4>
       Objects  gets  its work done by calling the Object rule on
       each of the source files.
       You could use the Object rule directly.
       For example, on Unix, you could use:
<PRE>
              Object foo.o : foo.c ;
</PRE>
	However, the Object rule does not provide suffixes, and
	it does not provide the grist needed to construct target
	identifiers if you are using the SubDir* rules.
	A portable and robust Jamfile would need to invoke Object thus:
	<PRE>
	      Object &lt;src!util&gt;foo$(SUFOBJ) : &lt;src!util&gt;foo.c ;
	</PRE>
	which is inelegant and clearly shows why using Objects
	is better than using Object.
	<P>
	If there's any advantage to the Object rule, it's
       that it doesn't require that the object name bear
       any relationship to the source.  It is  thus  possible  to
       compile  the  same file into different objects.  For example:

<PRE>
              Object a.o : foo.c ;
              Object b.o : foo.c ;
              Object c.o : foo.c ;
</PRE>
       This compiles foo.c (three times) into a.o, b.o, and  c.o.
       Later examples show how this is useful.
<P>
       The Object rule looks at the suffix of the source file and
       calls the appropriate rules to do  the  actual  preprocessing
       (if any) and compiling needed to produce the output object file.
       The Object rule is
       capable of the generating of an object file from  any
       type of source.  For example:
<PRE>
              Object grammar$(SUFOBJ) : grammar.y ;
              Object scanner$(SUFOBJ) : scanner.l ;
              Object fastf$(SUFOBJ) : fastf.f ;
              Object util$(SUFOBJ) : util.c ;
</PRE>
	An even more elegant way to get the same result is to let the
	Objects rule call Object:
	<PRE>
              Objects grammar.y scanner.l fastf.f util.c ;
	</PRE>
	<P>
       In  addition to calling the compile rules, Object sets up
       a bunch of variables specific to  the  source  and  target
       files.  (See Variables Used in Compiling, below.)
<P>
<H4>
   Cc, C++, Yacc, Lex, Fortran, As, etc. Rules
</H4>
<P>
       The Object rule calls compile rules specific to the suffix of
       the source file.  (You can see which suffixes are supported
       by looking at the Object rule definition in Jambase.)
       Because  the  extra  work  done  by  the
       Object rule, it is not always useful to call the compile
       rules directly.  But the adventurous  user  might  attempt
       it.  For example:
<PRE>
              Yacc grammar.c : grammar.y ;
              Lex scan.c : scan.l ;
              Cc prog.o : prog.c ;
</PRE>
       These examples individually run yacc(1), lex(1), and the C
       compiler on their sources.
<P>
<H4>
   UserObject Rule
</H4>
       Any files with suffixes not understood by the Object  rule
       are passed to the UserObject rule.  The default definition
       of UserObject simply emits a warning that  the  suffix  is
       not  understood.   This  Jambase rule definition is intended to be
       overridden in Jamrules with one that recognizes the project-specific
       source file suffixes. For  example:

<PRE>
	#In Jamrules:

              rule UserObject
              {
                  switch $(&gt;)
                  {
                  case *.rc   : ResourceCompiler $(&lt;) : $(&gt;) ;
                  case *      : ECHO "unknown suffix on" $(&gt;) ;
                  }
              }

              rule ResourceCompiler
              {
                  DEPENDS $(&lt;) : $(&gt;) ;
		  Clean clean : $(<) ;
              }

              actions ResourceCompiler
              {
                  rc /fo $(&lt;) $(RCFLAGS) $(&gt;)
              }


	#In Jamfile:

              Library liblock : lockmgr.c ;
	      if $(NT) { Library liblock : lock.rc ; }
</PRE>
<P>
	In this example, the UserObject definition in Jamrules
	allows *.rc files to be handle as regular Main and Library
	sources. The lock.rc file is compiled into lock.obj
	by the "rc" command, and lock.obj is archived into a library
	with other compiled objects.
<H4>
   LibraryFromObjects Rule
</H4>
       Sometimes the Library rule's straightforward compiling  of
       source  into  object modules to be archived isn't flexible
       enough.  The LibraryFromObjects rule  does  the  archiving
       (and  deleting)  job of the Library rule, but not the compiling.  
       The user can make use of the  Objects  or  Object
       rule for that.  For example:
<PRE>
              LibraryFromObjects libfoo.a : max.o min.o ;
              Object max.o : maxmin.c ;
              Object min.o : maxmin.c ;
              ObjectCcFlags max.o : -DUSEMAX ;
              ObjectCcFlags min.o : -DUSEMIN ;
</PRE>
       This  Unix-specific example compiles  the  same  source  file into 
       two different
       objects, with different compile flags, and archives  them.
       (The ObjectCcFlags rule is described shortly.)
       Unfortunately, the portable and robust implementation of the
       above example is not as pleasant to read:
       <PRE>
	      SubDir TOP foo bar ;
              LibraryFromObjects libfoo$(SUFLIB) : &lt;foo!bar&gt;max$(SUFOBJ) 
			                           &lt;foo!bar&gt;min$(SUFOBJ) ;
              Object &lt;foo!bar&gt;min$(SUFOBJ) : &lt;foo!bar&gt;maxmin.c ;
              Object &lt;foo!bar&gt;max$(SUFOBJ) : &lt;foo!bar&gt;maxmin.c ;
	      ObjectCcFlags &lt;foo!bar&gt;min$(SUFOBJ) : -DUSEMIN ;
	      ObjectCcFlags &lt;foo!bar&gt;max$(SUFOBJ) : -DUSEMAX ;
       </PRE>
       Note that, among other things, you must supply the library
       file suffix when using the LibraryFromObjects rule.
<P>
<H4>
   MainFromObjects Rule
</H4>
       Similar  to  LibraryFromObjects,  MainFromObjects does the
       linking part of the Main rule, but not the compiling.
       MainFromObjects  can be used when  there  are no
       objects at all,  and  everything  is  to  be  loaded  from
       libraries.  For example:
<PRE>
              MainFromObjects testprog ;
              LinkLibraries testprog : libprog ;
              Library libprog : main.c util.c ;
</PRE>
       On Unix, say, this generates a link command that looks like:
<PRE>
              cc -o testprog libprog.a
</PRE>
       Linking  purely  from  libraries is something that doesn't
       work everywhere: it depends on  the  symbol  "main"  being
       undefined when the linker encounters the library that contains 
       the definition of "main".
<P>
<H4>
   Variables Used in Compiling
</H4>
       The following variables control the  compiling  of  source
       files:
<P>
<CENTER>
<TABLE>
<TR><TD VALIGN=TOP>
              C++              
	      <TD><TD>The C++ compiler command
<TR><TD VALIGN=TOP>
              CC               
	      <TD><TD>The C compiler command
<TR><TD VALIGN=TOP>
              C++FLAGS       
	      <BR>
              CCFLAGS        
	      <TD VALIGN=TOP><TD VALIGN=TOP>Compile flags, used to
		 create or update compiled objects
<TR><TD>
              SUBDIRC++FLAGS 
	      <BR>
              SUBDIRCCFLAGS  
	      <TD VALIGN=TOP><TD VALIGN=TOP>Additonal compile flags
		for source files in this directory.
<TR><TD VALIGN=TOP>
              OPTIM            
	      <TD><TD>Compiler optimization flag. The Cc and C++ 
		actions use this as well as C++FLAGS or CCFLAGS.
<TR><TD VALIGN=TOP>
              HDRS           
	      <TD VALIGN=TOP><TD>Non-standard header directories; i.e.,
		the directories the compiler will not look in 
		by default and which therefore must be supplied
		to the compile command. These directories are
		also used by <b>jam</b> to scan for include files.
<TR><TD VALIGN=TOP>
              STDHDRS        
	      <TD VALIGN=TOP><TD>Standard header directories, i.e., the
		directories the compiler searches automatically.
		These are not passed to the compiler, but they
		are used by <b>jam</b> to scan for include files.
<TR><TD>
              SUBDIRHDRS     
	      <TD><TD>Additional paths to add to HDRS for source files
		in this directory.
<TR><TD>
              LEX              
	      <TD><TD>The lex(1) command 
<TR><TD>
              YACC             
	      <TD><TD>The yacc(1) command 
</TABLE>
</CENTER>
<P>
       The  Cc rule sets a target-specific $(CCFLAGS) to the current 
       value of $(CCFLAGS) and $(SUBDIRCCFLAGS).   Similarly
       for  the C++ rule.  The Object rule sets a target-specific
       $(HDRS) to  the  current  value  of  $(HDRS)  and  $(SUBDDIRHDRS).

<P>
       $(CC),  $(C++),  $(CCFLAGS),  $(C++FLAGS),  $(OPTIM),  and
       $(HDRS) all affect the  compiling  of  C  and  C++  files.
       $(OPTIM)  is  separate  from $(CCFLAGS) and $(C++FLAGS) so
       they can be set independently.
<P>
       $(HDRS) lists the directories to search for header  files,
       and  it  is used in two ways: first, it is passed to the C
       compiler (with the flag -I prepended); second, it is  used
       by  HdrRule  to  locate  the header files whose names were
       found when scanning source files.   $(STDHDRS)  lists  the
       header  directories  that  the  C  compiler  already knows
       about.  It does not need passing to the C compiler, but is
       used by HdrRule.
<P>
       Note that these variables, if set as target-specific variables, 
       must be set on the target,  not  the  source  file.
       The target file in this case is the object file to be generated.  
       For example:
<PRE>
              Library libximage : xtiff.c xjpeg.c xgif.c ;

              HDRS on xjpeg$(SUFOBJ) = /usr/local/src/jpeg ;
              CCFLAGS on xtiff$(SUFOBJ) = -DHAVE_TIFF ;
</PRE>
       This can be done more easily with the rules that follow.
<P>
<H4>
   ObjectCcFlags, ObjectC++Flags, ObjectHdrs Rules
</H4>
       $(CCFLAGS), $(C++FLAGS) and  $(HDRS)  can  be  set on object file
       targets
       directly, but  there are rules that allow these variables
       to be set by referring to the original source  file  name,
       rather  than  to  the  derived object file name.  ObjectCcFlags 
       adds object-specific flags to the $(CCFLAGS)  variable,  
       ObjectC++Flags  adds  object-specific  flags to the
       $(C++FLAGS) variable, and ObjectHdrs  add  object-specific
       directories to the $(HDRS) variable.  For example:
<PRE>
	#In Jamrules:
		if $(NT) { CCFLAGS_X = /DXVERSION ;	
			   HDRS_X = \\\\SPARKY\\X11\\INCLUDE\\X11 ;
		         }

	#In Jamfile:
              Main xviewer : viewer.c ;
              ObjectCcFlags viewer.c : $(CCFLAGS_X) ;
              ObjectHdrs viewer.c : $(HDRS_X) ;
</PRE>
	The ObjectCcFlags and ObjectHdrs rules take .c files
	as targets, but actually set $(CCFLAGS) and $(HDRS) values
	on the .obj (or .o) files. As a result, the action
	that updates the target .obj file uses the target-specific
	values of $(CCFLAGS) and $(HDRS).
<P>
<H4>
   SubDirCcFlags, SubDirC++Flags, SubDirHdrs Rules
</H4>
       These rules set the  values  of  $(SUBDIRCCFLAGS),  $(SUBDIRC++FLAGS)  
       and $(SUBDIRHDRS), which are used by the Cc,
       C++, and Object rules  when  setting  the  target-specific
       values  for $(CCFLAGS), $(C++FLAGS) and $(HDRS).  The SubDir 
       rule clears these variables out, and thus they provide
       directory-specific  values of $(CCFLAGS), $(C++FLAGS)  and
       $(HDRS).  For example:
<PRE>
	#In Jamrules:
              GZHDRS = $(TOP)/src/gz/include ;
	      GZFLAG = -DGZ ;
		
	#In Jamfile:
              SubDir TOP src gz utils ;

              SubDirHdrs $(GZHDRS) ;
              SubDirCcFlags $(GZFLAG) ;

	      Library libgz : gizmo.c ;
	      Main gizmo : main.c ;
	      LinkLibraries gizmo : libgz ;
</PRE>
	All .c files in this directory files will be compiled with
	$(GZFLAG) as well as the default $(CCFLAG), and the include
	paths used on the compile command will be $(GZHDRS) as well
	as the default $(HDRS).
<H2>
Header File Processing
</H2>
       One of the functions of the Object rule is set up 
       scanning of source
       files  for (C style) header file inclusions.  To do so, it
       sets the special variables $(HDRSCAN)  and  $(HDRRULE)
       as  target-specific  variables  on  the source file.  The
       presence of these variables triggers a  special  mechanism
       in  <B>jam</B> for scanning a file for header file inclusions and
       invoking a  rule  with  the  results  of  the  scan.   The
       $(HDRSCAN)  variable  is  set  to an egrep(1) pattern that
       matches "#include" statements in C source files,  and  the
       $(HDRRULE)  variable  is  set to the name of the rule that
       gets invoked as such:
<PRE>
              $(HDRRULE) source-file : included-files ;
</PRE>
       This rule is supposed to set up the  dependencies  between
       the  source  file and the included files.  The Object rule
       uses HdrRule  to  do  the  job.   HdrRule  itself  expects
       another  variable,  $(HDRSEARCH), to be set to the list of
       directories where the included files can be found.  Object
       does  this  as  well,  setting $(HDRSEARCH) to $(HDRS) and
       $(STDHDRS).
<P>
       The header file scanning occurs during the "file  binding"
       phase   of  <b>jam</b>,  which  means  that  the  target-specific
       variables (for the source file) are in effect.  To accomodate 
       nested includes, one of the HdrRule's jobs is to pass
       the target-specific values of $(HDRRULE), $(HDRSCAN),  and
       $(HDRSEARCH) onto the included files, so that they will be
       scanned as well.
<P>
<H4>
   HdrRule Rule
</H4>
	Normally, HdrRule is not invoked directly; the Object rule
	(called by Main and Library) invokes it.
	<P>
	If there are special dependencies that need to be set,
	and which are not set by HdrRule itself, you can define
	another rule and let it invoke HdrRule.  For example:

<PRE>
	#In Jamrules:
              rule BuiltHeaders
              {
                      DEPENDS $(&gt;) : mkhdr$(SUFEXE) ;
                      HdrRule $(&lt;) : $(&gt;) ;
              }

	#In Jamfile:
              Main mkhdr : mkhdr.c ;
              Main ugly : ugly.c ;

              HDRRULE on ugly.c = BuiltHeaders ;

</PRE>
       This example just says that the files included by "ugly.c"
       are  generated  by the program "mkhdr", which can be built
       from "mkhdr.c".  During the binding phase, <b>jam</b> will
       scan ugly.c, and if it finds an include file, ughdr.h,
       for example, it will automatically invoke the rule:
       <PRE>
              BuiltHeaders ugly.c : ughdr.h ;
       </PRE>
       By calling HdrRule at the end  of  BuiltHeaders,  
       all  the gadgetry of HdrRule takes effect and it
       doesn't need to be duplicated.
<P>
<H4>
   Variables Used for Header Scanning
</H4>
<CENTER>
<TABLE>
<TR><TD VALIGN=TOP>
              HDRPATTERN    
	      <TD><TD>Default scan pattern for "include" lines.
<TR><TD VALIGN=TOP>
              HDRSCAN         
	      <TD><TD>Scan pattern to use. 
		This is a special variable: during binding, if
		both HDRSCAN and HDRRULE are set, scanning is activated
		on the target being bound.
		The HdrRule and Object rules sets this
		to $(HDRPATTERN) on their source targets.
<TR><TD VALIGN=TOP>
              HDRRULE         
	      <TD><TD>Name of rule to invoked on files found in header
		scan. The HdrRule and Object rules set this to "HdrRule"
		on their source targets. This is also a special variable;
		it's the only <b>jam</b> variable that can hold the
		name of a rule to be invoked.
<TR><TD VALIGN=TOP>
              HDRSEARCH       
	      <TD><TD>Search paths for files found during header scanning.
		This is set from $(HDRS) and $(STDHDRS), which are 
		described in the Compiling section.
		<b>jam</b> will search $(HDRSEARCH) directories for
		the files found by header scans. 
</TABLE>
</CENTER>
<P>
       The  Object rule sets HDRRULE and HDRSCAN specifically for
       the source files to be scanned, rather than globally.   If
       they  were  set  globally,  jam  would attempt to scan all
       files, even library archives and executables,  for  header
       file  inclusions.   That  would  be  slow and probably not
       yield desirable results.
<P>
<H2>
Copying Files
</H2>
<H4>
   File Rule
</H4>
       The File rule copies one file to another.  The target name
       needn't  be the same as the source name.  For
       example:
<PRE>
	switch $(OS)
	{
           case NT*  : File config.h : confignt.h ;
	   case *    : File config.h : configunix.h ;
	}
	LOCATE on config.h = $(LOCATE_SOURCE) ;
</PRE>
	This creates a config.h file from either confignt.h or
	configunix.h, depending on the current build platform.
<P>
	The File rule does not
	use the LOCATE_SOURCE variable set by the
	SubDir rule (although it does use SEARCH_SOURCE), which
	means you have to set the copied file's output directory
	yourself. That's done by setting the special
	LOCATE variable on the target, as shown above,
	or with the MakeLocate rule described below.
<H4>
   Bulk Rule
</H4>
       The Bulk rule is a shorthand for many invocations  of  the
       File  rule when all files are going to the same directory.
       For example:
<PRE>
	#In Jamrules:
              DISTRIB_GROB = d:\\distrib\\grob ;

	#In Jamfile:
              Bulk $(DISTRIB_GROB) : grobvals.txt grobvars.txt ;
</PRE>
	This causes gobvals.txt and grobvars.txt to be copied
	into the $(DISTRIB_GROB) directory.
<H4>
   HardLink Rule
</H4>
       The Unix-only HardLink rule makes a hard link (using ln(1)) from the
       source  to  the  target,  if there isn't one already.  For
       example:
<PRE>
              HardLink config.h : configunix.h ;
</PRE>
<H4>
   Shell Rule
</H4>
       The Shell rule is like the File rule, except that on Unix it makes
       sure  the first line of the target is "#!/bin/sh" and sets
       the permission to make the file executable.  For example:
<PRE>
              Shell /usr/local/bin/add : add.sh ;
</PRE>
<P>
	You can also use $(SHELLHEADER) to dictate
	what the first line of the copied file will be.
       For
       example:
<PRE>
              Shell /usr/local/bin/add : add.awk ;
              SHELLHEADER on /usr/local/bin/add = "#!/bin/awk -f" ;
</PRE>
       This installs an awk(1) script.
<P>
<H4>
   Variables Used When Copying Files
</H4>
<CENTER>
<TABLE>
<TR><TD VALIGN=TOP>
              FILEMODE      
	      <TD><TD>Default file permissions for copied files
<TR><TD VALIGN=TOP>
              SHELLMODE     
	      <TD><TD>Default file permissions for Shell rule targets
<TR><TD VALIGN=TOP>
              MODE            
	      <TD><TD>File permissions set on files copied by
		File, Bulk, and Shell rules. 
       		File and Shell sets a target-specific MODE to the  current
       		value  of  $(FILEMODE) or $(SHELLMODE), respectively.  
<TR><TD VALIGN=TOP>
              SHELLHEADER     
	      <TD><TD>String to write in first line of Shell targets 
	      (default is #!/bin/sh).

</TABLE>
</CENTER>
<P>

<H2>
Installing Files
</H2>
Jambase provides a set of Install* rules to copy files
into an destination directory and set permissions on them.
On Unix, the install(1) program is used.
If the destination directory does not exist, <b>jam</b>
creates it first.
<P>
All files copied with the Install* rules are dependencies
of the <i>install</i> pseudotarget, which means that the
command "jam install" will cause the installed copies to
be updated. Also, "jam uninstall" will cause the installed
copies to be removed.
<P>
The Install* rules are:
<CENTER>
<TABLE>
<TR><TD VALIGN=TOP><B>InstallBin</B>
    <TD VALIGN=TOP>Copies file and sets its permission to $(EXEMODE).
		   You must specify the suffixed executable name. E.g.:
    <PRE>InstallBin $(BINDIR) : thing$(SUFEXE) ;
		   </PRE>

<TR><TD VALIGN=TOP><B>InstallFile</B>
    <TD VALIGN=TOP>Copies file and sets its permission to $(FILEMODE). E.g.:
    <PRE>InstallFile $(DESTDIR) : readme.txt ;
		   </PRE>

<TR><TD VALIGN=TOP><B>InstallLib</B>
    <TD VALIGN=TOP>Copies file and sets its permission to $(FILEMODE).
		   You must specify the suffixed library name. E.g.:
    <PRE>InstallLib $(LIBDIR) : libzoo$(SUFLIB) ;
		   </PRE>

<TR><TD VALIGN=TOP><B>InstallMan</B>
    <TD VALIGN=TOP>Copies file into the man<i>n</i>
		   subdirectory of the target directory
		   and sets its permission to $(FILEMODE). E.g.,
		   this copies foo.5 into the $(DESTDIR)/man5 directory:
    <PRE>InstallMan $(DESTDIR) : foo.5 ;
		   </PRE>

<TR><TD VALIGN=TOP><B>InstallShell</B>
    <TD VALIGN=TOP>Copies file and sets its permission to $(SHELLMODE). E.g.:
    <PRE>InstallShell $(DESTDIR) : startup ;
		   </PRE>

</TABLE>
</CENTER>
<P>
<P>
<H4>
   Variables
</H4>
       The following variables control the installation rules:
<P>
<CENTER>
<TABLE>
<TR><TD>
              INSTALL        
	      <TD><TD>The install program (Unix only)
<TR><TD>
              FILEMODE     
	      <TD><TD>Default file permissions on readable files. 
<TR><TD>
              EXEMODE      
	      <TD><TD>Default file permission executable files.
<TR><TD>
              SHELLMODE    
	      <TD><TD>Default file permission on shell script files.
<TR><TD>
              MODE           
	      <TD><TD>Target-specific file permissions
</TABLE>
</CENTER>
<P>
<P>
       The  Install  rules set a target-specific MODE to the current 
       value of $(FILEMODE),  $(EXEMODE),  or  $(SHELLMODE),
       depending on which Install rule was invoked.
<P>
       The  directory variables are just defined for convenience:
       they must be passed  as  the  target  to  the  appropriate
       Install  rule.   The $(INSTALL) and mode variables must be
       set (globally) before calling the Install rules  in  order
       to take effect.
<P>
<H2>
Miscellaneous Rules
</H2>
<H4>
Clean Rule
</H4>
<P>
The Clean rule defines files to be removed when you run "jam clean".
Any site-specific build rules defined in your Jamrules should invoke
Clean so that outputs can be removed. E.g.,
<PRE>
	rule ResourceCompiler
	{
	   DEPENDS $(<) : $(>) ;
	   Clean clean : $(<) ;
	}
</PRE>
<P>
<P>
Most Jambase rules invoke the Clean rule on their built targets,
so "jam clean" will remove all compiled objects, libraries,
executables, etc.
<P>
<H4>
MakeLocate Rule
</H4>
      MakeLocate is a single convenient rule that creates a directory,
      sets LOCATE on a target to that directory, and makes the directory
      a dependency of the target. It is used by many Jambase rules,
      and can be invoked directly, e.g.:
      <PRE>
		GenFile data.tbl : hxtract data.h ;
		MakeLocate data.tbl : $(TABLEDIR) ;
      </PRE>
      In this example, the File rule creates data.tbl from data.h.
      The MakeLocate causes data.tbl to be written into the $(TABLEDIR)
      directory; and if the directory doesn't exist, it is created first.
      <P>
      The MakeLocate rule invokes another Jambase rule, MkDir,
      to (recursively) create
      directories. MkDir uses the $(MKDIR) variable to determine the
      platform-specific command that creates directories.
<P>
<H4>
RmTemps Rule
</H4>
	Some intermediate files are meant to be temporary. 
	The RmTemps rule can be used to cause 
	<b>jam</b> to delete them after they are used. 
	<P>
	RmTemps must be:
	<UL>
	<LI>
	the last rule 
	invoked on the permanent file that uses
	the temporary file(s) 
	<LI>
	invoked with the permanent file as the output
	target and the temporary file(s) as the input target
	<LI>
	invoked with the exact target identifiers of
	the permanent file and the temporary file(s)
	</UL>
	For
	example: 
	<PRE>
		SubDir TOP src big ;
		GenFile big.y : joinfiles part1.y part2.y part3.y ;
		Main bigworld : main.c big.y ;
		RmTemps bigworld$(SUFEXE) : &lt;src!big&gt;big.y ;
	</PRE>
	This causes big.y to be deleted after it has been used to create
	the bigworld executable. 
	The exact target identifier of big.y is  &lt;src!big&gt;big.y
	(the GenFile and Main rules tack on the grist automatically);
	the exact target identifier of the bigworld executable
	is bigworld$(SUFEXE).
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